Woody,
Did you try checking your carb. drain screws? drain out the contents of each bowl into a small,shallow glass cup and see what comes out w/ the fuel,also check the sediment bowl on the petcock/fuel shutoff valve.
I think you may have a tankful of rust and sediment that needs to be cleared out and then have the fuel tank professionally lined to cover over any remaining rust.
The other items you might check are:a worn out float needle & seat or a float that is weighed down w/ excess fuel;either of those will require replacing the parts.
